This invention relates to the field of housings and chassis and more particularly to those housings and chassis that incorporate keypads and speakers and that find application in portable radio transceivers.
Portable radio transceivers usually incorporate an outer housing into which a chassis is inserted. The chassis typically includes a four sided frame, open in the middle, with a front and a rear plate or "shield" covering the opening in the frame. The chassis usually contains the majority of the electronic components while the remaining components are either mounted to the outer housing directly or placed on modules which are attached to the outer housing.
For example, when a portable radio requires a key pad for the entry of data, the key pad and associated electronics are usually assembled into a module that is inserted into and covers an aperture in the outer housing. The keypad module is typically secured to the outer housing with screws and an electrical connector interconnects the keypad module and chassis electronics. The outer housing can be made waterproof by the use of a rubber "O" ring seal between the keypad module and the outer housing.
During initial testing of the chassis or during repair, the chassis is normally removed from the outer housing. With the prior art keypad module, the keypad switches and associated electronics must be separated from the chassis, thereby making it difficult to test or repair the radio as a complete integrated unit. If all the electrical components could be attached to the chassis, however, testing and repair would be facilitated because the chassis would be a complete functional unit, even though it was removed from the outer housing. Furthermore, the connector between the keypad module and chassis could be eliminated, thereby reducing cost and complexity. Therefore, it would be advantageous if all the keypad electrical components could be placed on the chassis.
In most prior art portable radios the speaker is mounted directly to the housing, thereby requiring a connector and cabling between the chassis and the speaker. In some radios, however, the speaker is mounted to the outside surface of the front shield of the chassis. An aperture with a diameter slightly smaller than the diameter of the speaker is formed in the front shield, and the speaker is inserted into the aperture until the speaker rim contacts the outside surface of the front shield. Before being inserted into the aperture, a thin film of a compliant gasket material is applied to the rim of the speaker. A sheet of foam is then glued to the inside surface of the front shield and to the speaker, thereby securing the speaker to the front shield. The front shield is inserted into the frame, however, it is not secured to the frame in anyway, but is allowed to "float". The front shield is electrically "grounded" to the frame by two spring fingers which are soldered to one corner of the frame. The free ends of the spring fingers electrically contact the inside surface of the front shield.
When the chassis (which includes the frame, and front and rear shields) is inserted into the outer housing, the foam compresses forcing the gasket material on the rim of the speaker against the inside surface of the outer housing. When the chassis is completely inserted into the housing, the speaker is positioned over a speaker grille in the outer housing, and the gasket material, which is held in place by the compressed foam, forms an acoustic seal between the speaker and the outer housing. The acoustic seal maintains the sound pressure level of the speaker by preventing the loss of acoustic energy through any gap that may have existed between the speaker rim and the outer housing.
One disadvantage of the prior art speaker system is that the foam can lose its resiliency over time and particularly at low temperatures. With the resiliency gone, the speaker is no longer held against the inside surface of the outer housing and the acoustic seal is lost, thereby decreasing the amount of sound energy transmitted through the speaker grille. Another disadvantage is that before the chassis is inserted into the outer housing, the front shield is not restrained within the frame and must be held in place by the person assembling the radio in order to insert the chassis in the outer housing. It would be desirable if the front shield could be restrained within the frame, but still be allowed to move within well defined limits. Furthermore, to reduce manufacturing costs and complexity, it would be advantageous if the step of soldering the grounding fingers to the corner of the frame could be eliminated.